The objective of this proposal is to study the role of photodynamic action in the changes which occur to lens crystallins during aging and cataractogenesis. Photodynamic action is defined as the oxidation of a substrate by the interaction of light, a photosensitizer, and oxygen. A photodynamic system can potentially generate four active states of oxygen, namely: singlet oxygen, superoxide anion, hydrogen peroxide, and hydroxyl radical. One of the specific aims of this study is to determine the capacity of these photodynamically generated active states of oxygen to alter lens crystallins. Lens crystallins will be exposed to a photodynamic system in vitro and subsequently analyzed for structural modifications by techniques such as electrophoresis, isoelectric focusing, gel chromatography and spectrofluorometry. In previous experiments we have demonstrated that photodynamically generated singlet oxygen can effect an increase in non-tryptophan blue fluorescence and crosslinking of lens crystallins. By quantitating these changes with spectrofluorometry and gel scanning, action spectra will be determined for the photodynamically mediated increase in blue fluorescence and crosslinking of lens crystallins. Polarographic measurements of the PO2 levels required for the system will also be made. Another specific aim of this proposal is to further characterize some photosensitizers which are endogenous to the lens. Through a careful analysis of the role of photodynamic action in altering lens crystallins in vitro we hope to gain more insight into the changes which occur to lens crystallins during aging and cataractogenesis.